Homeostasis & Transport Ch.5

(5-1) Homeostasis Cell membranes control what goes in & out

Passive Transport Movement of materials across a cell membrane without the use of E (ATP) 4 Types: Diffusion Osmosis Facilitated Diffusion Ion Channels

Diffusion Movement of molecules from an area of high concentration to low conc.

Concentration Gradient Difference in conc. of molecules across a membrane “Down the gradient” Move from high to low conc.

Equilibrium Conc. is equal on both sides of the membrane Diffusion ends

Diffusion Across a Membrane Depends upon size, shape, & chemical makeup Easy to diffuse: Small Nonpolar (dissolve in lipids)

Osmosis Water diffusion across a membrane

Hypotonic Solution Solute conc. is higher inside & water conc. is higher outside the cell Water moves into the cell May cause cytolysis (cells burst)

Hypertonic Solution Solute conc. is higher outside & water conc. is higher inside the cell Water moves out of the cell May cause plasmolysis (cells shrink)

Isotonic Solution Solute & water conc.’s are equal on both sides of the membrane Equilibrium

Isotonic Hypertonic Hypotonic

How Cells Deal with Osmosis Contractile vacuoles: collect excess water & pump it out of the cell Requires E Turgor pressure: P that water exerts against the cell wall

Facilitated Diffusion Carrier proteins assist diffusion across a membrane Specific to certain molecules (glucose)

Diffusion via Ion Channels Ion channels assist diffusion across a membrane Some always open, others gated Common ions: Na+ K+ Cl- Ca2+

(5-2) Active Transport Movement of a substance across a cell membrane against a conc. gradient Requires E

Na-K Pump Carrier protein that transports K+ into & Na+ out of the cells Helps conduction of electrical impulses in nerve cells

Endocytosis Cell surrounds & engulfs substances 2 Types: Pinocytosis: fluids or solutes Phagocytosis: large particles

Exocytosis Vesicle inside a cell fuses w/ the cell membrane & releases contents outside of cell Proteins, waste, toxins